Nonwoven fabric and process for making the same

ABSTRACT

An elastically stretchable nonwoven fabric comprises elastically stretchable first fibers made of a first polymer and inelastically stretchable second fibers made of a second polymer. The second fibers are separably attached to the first fiber at attaching areas intermittently formed on the first fiber. Between the attaching areas neighboring to each other the second fibers are spaced apart from the first fiber and have lengths longer than that of the first fiber. One to sixteen of the second fibers are provided per each first fiber.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an elastically stretchablenonwoven fabric having a smooth touch to skin and also to a process formaking the same.

[0002] Japanese Patent Application Publication No. 1994-184897 A(Ref. 1) discloses an elastically stretchable web formed by laminating afibrous layer of elastically stretchable polymer with a fibrous layer ofinelastic stretchable polymer.

[0003] Japanese Patent Application Publication No. 1997-512313 A (Ref.2) also discloses an elastically stretchable web formed by laminatingthe fibrous layer of elastically stretchable polymer with the fibrouslayer of inelastic stretchable polymer.

[0004] In the web and the nonwoven fabric disclosed in the above-citedPublications, respectively, the fibrous layer made of elasticallystretchable polymer is exposed on the surface of the fabric. The fibersmade of such polymer exhibit a relatively high friction coefficient andcorrespondingly rough touch. The elastically stretchable web ornon-woven fabric formed by laminating the fibrous layers tend to be athick one.

[0005] Japanese Patent Application Publication No. 1992-11021 A (Ref. 3)discloses an elastically stretchable conjugated thread comprising acore-sheath-type conjugated fiber of which the core fiber is made ofelastically stretchable urethane and the sheath fiber is made ofinelastic stretchable polyamide.

[0006] Japanese Patent Application Publication No. 1997-316748 A (Ref.4) discloses an elastically stretchable fabric including acore-sheath-type conjugated filament as a weft. In this fabric, theelastomeric core and the non-elastomeric sheath of the filament areseparated from each other and the sheath slackens to form bellows-likewrinkles as the filament is drawn.

[0007] The conjugated thread and the fabric disclosed in the above-citedPublications use the core-sheath type conjugated fiber of which the coreis formed by elastomeric fiber and the sheath is formed bynon-elastomeric fiber. The sheath functions to cover the elasticallystretchable polymer, i.e., the elastomeric fiber and thereby to preventthe elastomeric fiber from coming in direct contact with the user'sbody. In this way, the conjugated thread as well as the fabric disclosedin the above-cited Publications are able to offer a smooth touch to theskin and a comfortable touch for the user's body. However, the sheathfiber presenting bellows-like wrinkles obstructs the core fiber fromelastically contracting and, in consequence, limits an extensioncoefficient as well as a contraction coefficient of the conjugatedthread and the fabric. The conjugated fiber has its sheath formed withthe bellows-like wrinkles and therefore it is difficult for theseconjugated thread and fabric to offer the soft and flexible touchpeculiar to the fiber having a small fineness.

[0008] Japanese Patent Publication No. 3262803 B (Ref. 5) discloses aninvention relating to multi-component thermoplastic continuous filamentsobtained by melt spinning, a product formed of such filaments and aprocess for forming such a product. According to the disclosure of Ref.5, multi-component thermoplastic filaments extruded from the extruder isintroduced through a quenching chamber into a Lurgi-duct within whichthe filaments are drawn and split under the effect of compressed airsupplied thereinto. The filaments split in this manner are accumulatedon a collecting surface formed by perforated screen or the like.According to the disclosure of Ref. 5, the multi-component thermoplasticfilaments are split to a plurality of more fine filaments within theLurgi duct and then formed into a nonwoven fabric. Respective componentsconstituting the multi-component thermoplastic filament appear on thesurface of this nonwoven fabric in a form of more fine filaments inaccordance with the mixing proportion of these components. If one of thecomponents is a thermoplastic elastomer, the filament of such athermoplastic elastomer will be exposed on the surface of the nonwovenfabric and a wearer of a wearable article made of the nonwoven fabricmay experience a rough touch with poor slip properties of the nonwovenfabric depending on a proportion of the thermoplastic elastomerfilament.

[0009] Japanese Patent Application Publication No. 1997-291454 A (Ref.6) discloses an invention relating to an elastically stretchablenonwoven fabric. According to the disclosure of Ref. 6, the elasticallystretchable nonwoven fabric is formed using elastically stretchableconjugated fibers consisting of a hard elastic member comprisingcrystalline polypropylene as a first component and a thermoplasticelastomer as a second component. The conjugated fibers may be selectedfrom a group including those of various types such as side-by-side andsheath-and-core. Such conjugated fibers can be finished into nonwovenfabric by various processes such as spun bonding and thermal bondingprocesses. According to Ref. 6 the elastically stretchable conjugatedfiber consisting of the hard elastic member comprising polypropylene asthe first component and the thermoplastic elastomer as the secondcomponent are intermittently welded into an elastically stretchablenonwoven fabric. The circumferential surface of the conjugated fiber isdefined by zones occupied by polypropylene and zones occupied by theelastomer. In this case the thermoplastic elastomer is inevitablyexposed on the surface of the nonwoven fabric. Consequently, thisnonwoven fabric may have a rough touch and poor slip properties. Ref. 6describes as one of embodiments a sheath-and-core type conjugated fiberof which the sheath is formed by polypropylene as the first componentand the core is formed by the elastomer comprising ethylene-α-olefincopolymer as the second component. The elastic stretchability of such aconjugated fiber is governed by the stretchability of the hard elasticmember comprising polypropylene and the stretchability of the elastomermight be thereby suppressed.

REFERENCES

[0010] [Ref. 1] Japanese Patent Application Publication No. 1994-184897A

[0011] [Ref. 2] Japanese Patent Application Publication No. 1997-512313A

[0012] [Ref. 3] Japanese Patent Application Publication No. 1992-11021 A

[0013] [Ref. 4] Japanese Patent Application Publication No. 1997-316748A

[0014] [Ref. 5] Japanese Patent Publication No. 3262803 B

[0015] [Ref. 6] Japanese Patent Application Publication No. 1997-291454A

SUMMARY OF THE INVENTION

[0016] It is an object of the present invention to provide a novelelastic nonwoven fabric adapted to have a broad elastic extension rangeas well as a broad elastic contraction range and to offer a smooth touchto the skin.

[0017] The present invention has a first aspect relating to a nonwovenfabric and a second aspect relating to a process for making the nonwovenfabric.

[0018] According to the first aspect of the invention, there is providedan elastically stretchable nonwoven fabric comprising elasticallystretchable first fibers made of a first polymer and inelasticallystretchable second fibers made of a second polymer.

[0019] The improvement according to the first aspect of the invention ischaracterized in that the nonwoven fabric has first and second surfacesas viewed in its thickness direction, the first and second surfacesextending in parallel to each other, the second fiber is attached to thefirst fiber at attaching areas formed intermittently along the firstfiber and spaced apart from the first fiber between each pair of theneighboring attaching areas, each segment of the second fiber spacedapart from the first fiber between each pair of the neighboringattaching areas being longer than an associated segment of the firstfiber, and the number of the second fiber is in a range of 1 to 16 pereach first fiber.

[0020] The first aspect of the invention can be implemented inpreferable manners as follows:

[0021] (1) the first and second fibers intersect with each other in sucha manners that the first fiber lies inside and the second fiber liesoutside in any one of the first and second surfaces;

[0022] (2) the first fiber has on its circumferential surface firstcurved surfaces each bulging radially outward from an axis of the firstfiber and second curved surfaces each depressed radially toward the axisof the first fiber, the first and second curved surfaces alternatelyappearing in a circumferential direction of the first fiber, and eachpair of the first curved surfaces neighboring to each other in thecircumferential direction cooperate with the second curved surface lyingbetween the pair of the first curved surfaces neighboring to each otherto form a groove extending in a longitudinal direction of the firstfiber so that the second curved surface defines a bottom of the groove.In the case that the nonwoven fabric having such a first fiber is usedfor a wearable article, these are little chances where the first fibercontacts the skin of a wearer of the article, because the curvedsurfaces of the first fiber cannot contact the skin.

[0023] (3) one of the first and second surfaces has a slip angle of 25°to 40°. The nonwoven fabric having the slip angle of such a range issuitable for a wearable article and other products.

[0024] (4) the first polymer is selected from the group consisting ofthermoplastic polyurethane and thermoplastic polyurethane containing alubricant and the second polymer is selected from the group consistingof polyolefin-based polymer and polyamide-based polymer.

[0025] The object set forth above is achieved, according to the secondaspect of the invention, by an improvement in a process for making anelastically stretchable nonwoven fabric formed by elasticallystretchable first fibers made of a first polymer and inelasticallystretchable second fibers made of a second polymer.

[0026] The improvement according to the second aspect of the inventionis characterized by that feeding, in a machine direction, a plurality ofconjugated fibers each consisting of a first fibrous component made ofthe first polymer and a second fibrous component extending in parallelto and releasably attached to a surface of the first fibrous componentand thereby forming a web from the conjugated fibers having a basisweight in a range of 10 to 500 g/m², forming the web with a plurality ofattaching areas intermittently formed in at least one direction of themachine direction and a cross direction intersecting orthogonally themachine direction so that the conjugated fibers can not be separated onefrom another at the attaching areas, stretching the web at least in theone direction within an elastic range of the first fibrous component andunder a failure point of the second fibrous component and therebyseparating the first and second fibrous components one from anotherbetween each pair of the attaching areas neighboring to each other andpermanently deforming the second fibrous component; and allowing the webto contract under an elastic recovery force of the first fibrouscomponent so that the first fiber may be obtained from the first fibrouscomponent, the second fiber may be obtained from the second fibrouscomponent and the nonwoven fabric may be obtained from the web.

[0027] The second aspect of the invention can be implemented inpreferable manners as follow:

[0028] (1) the first fibrous component of the conjugated fiber has onits circumferential surface first curved surfaces each bulging radiallyoutward from an axis of the first fibrous component and second curvedsurfaces each depressed radially toward an axis of the first fibrouscomponent, the first and second curved surfaces alternately appearing inthe circumferential direction of the first fibrous component, and eachpair of the first curved surfaces neighboring to each other in thecircumferential direction cooperate with the second curved surface lyingbetween the pair of the first curved surfaces neighboring to each otherto form a groove extending in the longitudinal direction of the firstfibrous component so that the second fibrous component extends inparallel to the first fibrous component in the groove.

[0029] (2) the circumferential length of the conjugated fiber occupiedby the second fibrous component is in a range of 40 to 90% of the wholecircumferential length of the conjugated fiber.

[0030] (3) the number of the second fibrous component constituting theconjugated fiber is in a range of 1 to 16 per one of the first fibrouscomponent.

[0031] (4) the first polymer is selected from the group consisting ofthermoplastic polyurethane and thermoplastic polyurethane containing alubricant and the second polymer is selected from the group consistingof polyolefin-based polymer and polyamide-based polymer.

[0032] In the present invention the slip angle is measured in anapparatus depicted by an accompanying drawing, i.e. FIG. 11. Themeasuring method of the slip angle is included in the explanation ofFIG. 11.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a perspective view showing a typical embodiment of anonwoven fabric;

[0034]FIG. 2 is a photograph showing cross-sections of conjugatedfibers;

[0035]FIG. 3 is a diagram tracing the conjugated fibers in photograph ofFIG. 2;

[0036]FIG. 4 is a scale-enlarged plan view showing a part of FIG. 1;

[0037]FIG. 5 is a sectional view taken along a line V-V in FIG. 4;

[0038]FIG. 6 is a scale-enlarged portion of FIG. 5;

[0039]FIG. 7 is a view similar to FIG. 5 illustrating a relativeposition of the respective fibers when the nonwoven fabric is stretched;

[0040]FIG. 8 is a photograph similar to FIG. 2 showing a preferredembodiment of the present invention;

[0041]FIG. 9 is a diagram similar to FIG. 3 showing the preferredembodiment;

[0042]FIGS. 10A, 10B and 10C are sectional views of the conjugatedfibers; and

[0043]FIG. 11 is a side view of a tester.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Details of the nonwoven fabric and the process for making thesame according to the present invention will be more fully understoodfrom the description given hereunder with reference to the accompanyingdrawings.

[0045] A substantially hexahedral fragment of nonwoven fabric 1 shown inFIG. 1 in a perspective view has upper and lower surfaces 2, 3 whichextend parallel to each other and define the thickness of the nonwovenfabric 1 and side surfaces defined by cut surfaces 4 a, 4 b, 4 c, 4 deach intersecting the upper and lower surfaces 2, 3. The nonwoven fabric1 comprises elastically stretchable fibers 11 made of a firstthermoplastic polymer, inelastically stretchable fibers 12 made of asecond thermoplastic polymer and conjugated fiber regions 13 formed bythe elastic fibers 11 and the inelastic fibers 12 which are joinedtogether side by side. In the nonwoven fabric 1, these fibers 11, 12 andthe conjugated fiber regions 13 are welded, adhesively bonded ormechanically intertwined together at a plurality of attaching area 16 sothat these fibers 11, 12 and the conjugated fiber regions 13 may besubstantially fixed in the area 16. The elastic fibers 11 and theinelastic fibers 12 are obtained by splitting each conjugated fiber 13 acorresponding to each of the conjugated fiber regions 13 into a fibercomponent 21 and a fiber component 22 (see FIG. 2) during a productionprocess as will be described later. As will be seen in FIG. 1, theconjugated fiber regions 13 principally lie in the vicinity of therespective attaching area 16.

[0046] In the nonwoven fabric 1, the elastic fibers 11 have a finenessin a range of 0.1 dtx to 10 dtx and the inelastic fibers 12 have afineness in a range of 0.05 dtx to 2 dtx. The fineness of the inelasticfiber 12 is preferably smaller than the fineness of the elastic fiber11. Except for the area 16, in the surrounding area of each of theelastic fibers 11, one to sixteen of the inelastic fibers 12 extends orextend between the neighboring areas 16, for example, the area 16 a andthe area 16 b depicted in FIG. 1. In a preferred embodiment of thenonwoven fabric 1, at least three inelastic fibers 12 a, 12 b, 12 c liein the surrounding area of the individual elastic fiber 11 a (see FIG.5) and wrap around this elastic fiber 11 a. In the vicinity of the areas16 a and 16 b, the inelastic fibers 12 a, 12 b, 12 c are branched andspaced apart from the elastic fiber 11 a. Thus the elastic fiber 11 andthe inelastic fibers 12 are repeatedly joined together (at the areas 16)and spaced apart from each other in a longitudinal direction of theelastic fiber 11. Between the neighboring areas 16 a and 16 b, eachsegment of the inelastic fibers 12 a, 12 b, 12 c is longer than thesegment of the elastic fiber 11 a, and the elastic fiber 11 a issubstantially rectilinear and the inelastic fibers 12 a, 12 b, 12 cdescribe various curves, respectively. On the upper surface 2 the ratioof the number of the elastic fiber 11 a to the number of the inelasticfibers 12 a, 12 b, 12 c is approximately 1:3. The elastic fiber 11 a andthe inelastic fibers 12 a, 12 b, 12 c have ends thereof exposed on thecut surface 4 a and the number of these ends approximately correspondsto the number of the elastic fibers 11 a and the inelastic fibers 12 a,12 b, 12 c. In other words, a ratio of the ends of the elastic fibers 11a to the ends of the inelastic fibers 12 a, 12 b, 12 c exposed on thecut surface 4 a is approximately 1:3.

[0047] Uses of the nonwoven fabric 1 are not specified. The nonwovenfabric 1 can be used for a wearable article, for example, a disposablediaper, disposable pants or a disposable medical gown, and householdgoods, for example, disposable wipes. In the nonwoven fabric 1 used inthese fields it is preferable that a straight distance between theneighboring attaching areas 16 a and 16 b on the elastic fiber 11 a is0.5-10 m, and that the lengths of the inelastic fibers 12 a, 12 b, 12 cbetween the neighboring attaching areas 16 a and 16 b are 1.2-5 times ofthe length of the associated elastic fiber 11 a.

[0048] The elastic fibers 11 are elastically stretched when the nonwovenfabric 1 of the arrangement as has been described above is held with thehands and pulled in a direction A or in a direction B intersectingorthogonally the direction A, whereupon the inelastic fibers 12 areoriented to extend in the direction A or in the direction B. Uponreleasing from the pulled condition, an elastic recovery force of theelastic fibers 11 causes the nonwoven fabric 1 to shrink to the state ofFIG. 1. It is well known that such an elastic material as the elasticfiber 11 has a rubbery rough touch, but the presence of the pluralinelastic fibers 12 wrapping around the respective elastic fibers 11 iseffective to provide the upper and lower surfaces 2, 3 of the nonwovenfabric 1 with a smooth and slipping touch similar to that of theinelastic fiber 12. In addition, the smooth and slipping touch of thenonwoven fabric 1 of the present invention can be controlled by afineness, a shape of the cross section and a number of the inelasticfiber 12. The fineness of the inelastic fibers 12 may be minimized, forexample, in the order of 0.5 dtx to 1.5 dtx to make the touch of theupper and lower surfaces 2, 3 more smooth and flexible.

[0049]FIG. 2 is a photograph showing cross-sections of conjugated fibers13 a used to make the nonwoven fabric 1 and FIG. 3 is a diagram tracingthe conjugated fibers 13 a in the photograph of FIG. 2. A plurality ofthe conjugated fibers 13a appearing in FIG. 2 are substantiallyidentical one to another. Each of these fibers 13 a has a diameter of 25μm to 30 μm and comprises a single elastic fiber component 21 and threeinelastic fiber components 22 separably attaching to the surface of theelastic fiber component 21 substantially at regular intervals in acircumferential direction. The conjugated fiber 13 a is substantiallyidentical to the conjugated fiber component 13 depicted in FIG. 1 inconstruction as well as in composition. The conjugated fiber 13 a can beobtained by extruding simultaneously an elastic thermoplastic polymer toform the elastic fiber component 21 and an inelastic thermoplasticpolymer to form the inelastic fiber component 22 through nozzles of anextruder for melt spinning well known in the art.

[0050] The elastic fibrous component 21 has on its circumferentialsurface first curved surface portions 51 each bulging radially outwardfrom an axis of the elastic fibrous component 21 and second surfaceportions 52 each depressed radially toward the axis of the elastic firstfibrous component 21 so that these first and second surface portions 51,52 alternately appearing in the circumferential direction of the elasticfibrous component 21. Each pair of first surface portions 51, 51neighboring to each other in the circumferential direction cooperatewith the second surface portion 52 lying between the pair of neighboringfirst surface portions 51 to form a groove 53 wherein the second surfaceportion 51 defines a bottom of the groove 53 and a total of threegrooves 53 a, 53 b, 53 c extend in the longitudinal direction of theelastic fibrous component 21. The inelastic fibrous component 22comprises three inelastic fibrous components 22 a, 22 b, 22 c extendingin the longitudinal direction of the elastic fibrous component 21 in thegrooves 53 a, 53 b, 53 c, respectively.

[0051] The first polymer to be used to obtain the elastic fibercomponent 21 includes a thermoplastic polyurethane, a thermoplasticpolyurethane containing lubricant and any other thermoplasticelastomers. The second polymer to be used to obtain the inelastic fibercomponent 22 includes thermoplastic polymer which is incompatible withthe first polymer and stretches inelastically. The term “incompatible”used herein means that a conjugation strength of the inelastic fibercomponent 22 to the elastic fiber component 21 is relatively low and theinelastic fiber component 22 can be easily separated or split from theelastic fiber component 21, when the conjugated fiber 13 a is stretched.The second polymer having such properties may be selected from the groupincluding polyolefine polymer such as polyethylene or polypropylene andpolyamide polymer such as nylon. Either homopolymer or copolymer ofpolypropylene can be used. The inelastic fiber 12 of polypropylene haspreferably crystallinity less than 30% and, more preferably, less than20% and does not include a fiber to be deemed as a hard elastic fiber.The crystallinity of the inelastic fiber 12 is measured by a DSC methodin the present invention. The first elastic fiber component 21 may bemade by thermoplastic polyurethane containing a lubricant such as fattyamide to facilitate the inelastic fiber component 22 to be separatedeasily from the elastic fiber component 21.

[0052] An example of the elastic fibrous component 21 is a thermoplasticpolyurethane whose melt viscosity based on JIS K 7311 is 23×10³-180×10³poise. An example of the inelastic fiber component 22 is a polypropylenewhose Melt Flow Rate (MFR) is 30 at 230° C. and 2.16 kg/cm². Apreferable weight ratio of the elastic fibrous component 21 to theinelastic fibrous component 22 is 20:80-90:10. In a preferable case ofthe conjugated fiber 13 a, the inelastic fibrous components 22associated with each elastic fibrous component 21 have a circumferentiallength occupying 40% to 90% of the whole circumferential length of thecomposite fiber 13 a. The areas and shapes of the elastic fibrouscomponent 21 and the inelastic fibrous component 22 in the cross-sectionof the conjugated fiber 13 a are formed in such a way that the elasticfiber 11 from the elastic fibrous component 21 may have a fineness of0.1-10 dtx and the inelastic fiber 12 from the inelastic fibrouscomponent 22 may have a fineness of 0.05-2 dtx and less than that of theelastic fiber 11. A preferable inelastic fibrous component 22 may have aflat cross-section such as an oval shape and the inelastic fiber 12derived from the inelastic fibrous component 22 may have also a flatcorss-section. If the inelastic fiber 12 has a flat cross-section, thelength of the long axis may be longer than two times of the length ofthe short axis so that the inelastic fiber 12 can be easily bent.

[0053] Using such a conjugated fiber 13 a, the nonwoven fabric 1 of FIG.1 is formed in a manner as will be described. Preferably, the conjugatedfiber 13 a of continuous type is used. A plurality of conjugated fibers13 a is supplied in a machine direction to make a web having a basisweight of 10 g/m² to 500 g/m². In the course of making such a web, theattaching areas 16 depicted in FIG. 1 in which the conjugated fibers 13a are joined or intertwined together in an inseparable manner may beformed intermittently in one of the machine direction and the crossdirection intersecting orthogonally the machine direction by anappropriate treatment, for example, by embossing the web under heatingor by jetting high pressure columnar water to the web or by blowing aheated air to the web. This web may be stretched within an elastic rangeof the elastic fibrous component 21 and under a failure point of theinelastic fibrous component 22, for example, by 70% or more in onedirection or in two directions along which the attaching areas 16 areformed intermittently. Thereafter, the web is relieved from thestretched condition and is contracted by the elastic recovery force ofthe elastic fiber component 21 to obtain the nonwoven fabric 1 depictedin FIG. 1. Between each pair of the neighboring attaching areas 16, 16,for example, the areas 16 a and 16 b in FIG. 1, the conjugated fiber 13a is separated or split along the interfaces of the elastic fibercomponent 21 and the inelastic fiber components 22 into one elasticfiber 11 and three inelastic fiber components 12. At the same time, theinelastic fibers 12 also elongate so as to be permanently deformed and adiameter of each inelastic fiber 12 is reduced. In the nonwoven fabric 1obtained by contracting the web, between each pair of the neighboringareas 16, 16, the elastic fibers 11 contract so as to describe asubstantially straight line or a gentle curve while each of theinelastic fibers 12 longer than the elastic fiber 11 describes a curvewhich is more complicated than the elastic fibers 11 and intersect theelastic fibers 11 and the inelastic fibers 12.

[0054]FIG. 4 is a scale-enlarged plan view showing the elastic fibers 11a representing the elastic fiber 11 and the inelastic fibers 12 a, 12 b,12 c representing the inelastic fiber 12 on the upper surface 2 of thenonwoven fabric 1 of FIG. 1 obtained in the manner as has been describedabove, and FIG. 5 is a sectional view taken along a line V-V in FIG. 4.In the vicinity of the areas 16 a, 16 b, as will be apparent from FIG.4, the elastic fiber component 21 and the inelastic fiber components 22of the conjugated fiber 13 a are not separated, and therefore, theconjugated fiber 13 a forms the conjugated fiber regions 13. Betweeneach pair of the neighboring areas 16 a, 16 b on the elastic fiber 11 aseparated from the inelastic fibers 12 a, 12 b, 12 c, the elastic fiber11 a describes a substantially straight line while the inelastic fibers12 a, 12 b, 12 c describe various curves. The inelastic fiber 12 b areintersecting the elastic fiber 11 a so as to provide crossing points. Atthe crossing points the elastic fiber 11 a lies inside and the inelasticfiber 12 b lies outside in the thickness direction of the nonwovenfabric 1. On the cut surface shown in FIG. 5, the inelastic fibers 12 a,12 b, 12 c are distributed around the elastic fiber 11 a so as tosurround the elastic fiber 11 a.

[0055]FIG. 6 is a scale-enlarged perspective view of the elastic fiber11 a of FIG. 5. The circumferential surface of the elastic fiber 11 a isdefined by first curved surface portions 61 each radially bulgingoutward from an axis of the elastic fiber 11 a with a relatively smallcurvature radius and second curved surface portions 62 each radiallydepressed toward the axis of the elastic fiber 11 a so that these firstand second curved surface portions 61, 62 alternately appear on thecircumferential surface of the elastic fiber 11 a. The second curvedsurface portion 62 lies between each pair of the first curved surfaceportions 61 neighboring to each other in the circumferential directionand these first and second curved surface portions 61, 62 cooperatetogether to form a groove 63 extending in the longitudinal direction ofthe elastic fiber 11 a. These first curved surface portion 61, secondcurved surface portion 62 and groove 63 respectively correspond to thefirst surface portion 51, the second surface portion 52 and the groove53 of the conjugated fiber 13 a depicted by FIG. 3.

[0056] With a wearable article made of the nonwoven fabric 1 includingthe elastic fiber 11 and the inelastic fiber 12 depicted in FIGS. 4, 5and 6, the article wearer's skin readily comes in contact with theinelastic fibers 12 a, 12 b, 12 c rather than with the elastic fiber 11a. Consequently, a touch and slip properties of the nonwoven fabric 1are similar to those of the inelastic fiber 12. This is very true, whenthe number of the inelastic fibers 12 intersecting the elastic fiber 11a is relatively large as in the case depicted in FIG. 4 and the elasticfiber 11 a having a rough touch and poor slip properties to the articlewearer's skin is embedded among the inelastic fibers 12 on the uppersurface 2 of the nonwoven fabric 1. As will be apparent from FIG. 6, theelastic fiber 11 a comes in contact with the article wearer's skin 69indicated by imaginary lines merely in the vicinity of the first curvedsurface portions 61 but the second curved surface portions 62 rarelycomes in contact with the skin 69. In this way, the circumferentialsurface of the elastic fiber 11 a possibly coming in contact with theskin 69 is limited to an extremely small area having a small curvatureradius. Compared to an elastic fiber having a circular cross-section ofthe same area as that of the elastic fiber 11 a, the surface area of theelastic fiber 11 a coming in contact with the skin 69 is substantiallyreduced. The smaller the surface area of the elastic fiber 11 a possiblycoming in contact with the skin 69 is, the higher the smooth touch andslip properties of the nonwoven fabric 1 to the article wearer's skin 69are. Even if the elastic fiber 11 a comes in contact with the skin 69, agap is left in many cases between the skin 69 and the grooves 63 of theelastic fiber 11 a and such a gap serves to relieve the skin 69 from ahigh humid condition since the gap allows a vapour generated within thearticle to escape outward. The nonwoven fabric 1 according to theinvention can be implemented also in a manner that not the upper surface2 but the lower surface 3 is constructed as depicted in FIG. 1 or theboth surfaces 2, 3 are constructed as depicted in FIG. 1.

[0057]FIG. 7 is a view similar to FIG. 5 showing the nonwoven fabric 1being pulled in the direction A indicated in FIG. 4. The inelasticfibers 12 a, 12 b, 12 c of FIG. 5 move in directions indicated by arrowsP, Q, R and get nearer to the elastic fiber 11 a as the elastic fiber 11a is stretched in the direction A so that these inelastic fibers 12 a,12 b, 12 c may closely surround the elastic fiber 11 a as shown in FIG.7. If most of the inelastic fibers 12 of FIG. 7, orientate in thedirection A, the touch and slip properties of the nonwoven fabric 1 maybe further similar to the smooth touch and high slip properties of theinelastic fibers 11.

[0058]FIGS. 8 and 9 are views similar to FIGS. 2 and 3, exemplarilyshowing the conjugated fiber 13 a suitably used in the presentinvention. This conjugated fiber 13 a has a diameter of about 15μ andconsists of the elastic fibrous component 21 presenting a semicircularcross-section and the inelastic fibrous component 22 presenting asemicircular cross-section which are separably attached together. Theconjugated fiber 13 a thus presents a substantially circularcross-section and the inelastic fibrous component 22 appearing on acircumferential surface of this conjugated fiber 13 a occupiesapproximately 50% of the circumferential length of the conjugated fiber13 a. Also in the nonwoven fabric 1 obtained from the web comprisingthese conjugated fibers 13 a by stretching the web and then allowing theweb to contract, a length of the inelastic fiber derived from theinelastic fibrous component 22 is longer than the elastic fiber derivedfrom the elastic fibrous component 21. With such inelastic fibersflexing and/or curving so as to intersect the elastic fibers, theinelastic fibers function to prevent the elastic fibers from coming indirect contact with the article wearer's skin. Consequently, thenonwoven fabric obtained from these conjugated fibers 13 a exhibits asmooth touch and high slip properties to the article wearer's skinalthough a level of its slip properties can not be comparative to thoseexhibited by the nonwoven fabric 1 depicted in FIG. 1.

[0059] Since the nonwoven fabric 1 of the invention may be formed usingthe web of the conjugated fiber 13 a comprising the elastic fibrouscomponent 21 having the groove 53 as shown in FIG. 3 and the inelasticfibrous component 22 extending in this groove 53, it is easy to obtainthe inelastic fiber 12 which has a fineness smaller than a fineness ofthe elastic fiber 11.

[0060]FIGS. 10A, 10B and 10C exemplarily illustrate the cross-sectionsof the conjugated fibers 13 a. The conjugated fiber 13 a depicted inFIG. 10A presents a cross-section distinguished from that of theconjugated fiber 13 a depicted in FIG. 9 in that the elastic fibrouscomponent 21 is formed with a single groove 53. In the case of theconjugated fiber 13 a depicted in FIG. 10B, the elastic fibrouscomponent 21 is formed with a pair of grooves 53. Finally, in the caseof the conjugated fiber 13 a depicted in FIG. 10C, the elastic fibrouscomponent 21 is formed with four grooves 53. In this manner, it ispossible without departing from the scope of the invention to form theelastic fibrous component 21 with a selective number of the grooves 53in a range of one to sixteen.

[0061]FIG. 11 is a side view of a tester 70 used in the presentinvention to evaluate the nonwoven fabric with respect to its slipproperties. The tester 70 comprises a plate 71 driven by an electricmotor 73 so that its angle a of a gradient relative to the horizontalplane may be increased at a predetermined rate and a block 72 to becovered with the nonwoven fabric to be evaluated. The plate 71 has itsupper surface formed of stainless steel having a surface roughness of12.5s as measured in accordance with JIS B 0601. The block 72 is made ofstainless steel having a weight adjusted to exert a surface pressure of10 g/cm² upon the nonwoven fabric. The nonwoven fabric is attached tothe block 72 so as to cover the entire lower surface of the block 72.The plate 71 supporting the block 72 is rotated around a pivot 74 sothat the angle α increases at a rate of 2°/sec until the block 72 beginsto slip over the upper surface of the plate 71. The angle α at which theblock 72 begins to slip is defined as a slip angle α_(s). The smallerthe value of α_(s) is, the higher the slip properties relative to thearticle wearer's skin are. Based on the tester 70, clothing fabric formen's and women's shirts and pants as undergarments made of 100% cottonexhibit the slip angle α_(s) in a range of about 21° to about 25°.

[0062] TABLE 1 indicates the slip angle α_(s) exhibited by the examplesof nonwoven fabric of the conjugated fiber 13 a depicted in FIGS. 2 and3 and control nonwoven fabrics. The nonwoven fabrics of the inventionwere obtained by subjecting the web having a basis weight of 50 g/m² toheat embossing both in the machine direction and in the cross direction.The conjugated fiber 13 a consisted of thermoplastic polyurethane andpolypropylene at a weight ratio in a range of 84.4:15.6 to 67.9:32.1 andpolypropylene occupied about 70 to 90% of the circumferential length ofthe conjugated fiber 13 a. The comparative embodiments of nonwovenfabric were made of thermoplastic polyurethane fiber or polypropylenefiber and obtained by subjecting the web having a basis weight of 50g/m² to heat embossing in the same manner as in the case of embodimentsof the invention. Both in the embodiments of the invention and in thecomparative embodiments, a plurality of heat embossed zones each of 0.3mm² were formed at a pitch of 2 mm in the machine direction as well asin the cross direction. As will be apparent from TABLE 1, the slip angleα_(s) of the nonwoven fabric 1 depends on the percentage by whichpolypropylene as the inelastic fibrous component 22 occupies thecircumferential length of the conjugated fiber 13 a. In other words, theinvention allows the slip angle α_(s) of the nonwoven fabric 1 to becontrolled by adjusting the proportion of the inelastic fibrouscomponent 22 occupying the circumferential length of the conjugatedfiber 13 a. When the nonwoven fabric 1 is used in a wearing article, theslip angle α_(s) of the upper surface 2 and/or the lower surface 3 iscontrolled preferably in a range of 25° to 40°.

[0063] In order to control the slip angle α_(s) of the nonwoven fabric1, it is possible without departing from the scope of the invention touse, in addition to those indicated as the embodiments, the conjugatedfiber 13 a consisting of thermoplastic polyurethane and polypropylene ata weight ratio in a range of 20:80 to 90:10. It is also possible to usethe conjugated fiber 13 a in which polypropylene occupies 40 to 90% ofthe circumferential length of this conjugated fiber 13 a. TABLE 1 Lengthoccupied by polypropylene in the whole Constituents of peripheralconjugated fiber (wt %) length of Slip Thermoplastic conjugate anglepolyurethane Polypropylene fiber (%) α_(s) Example 84.4 15.6 70.92 39.31 Example 76.5 23.5 75.04 34.3 2 Example 67.9 32.1 86.07 30.3 3 Control100 — 0 49.1 1 Control — 100 100 21.3 2

[0064] The nonwoven fabric of the present invention can be usedindustrially for disposable wearable articles and the nonwoven fabriccan be industrially manufactured through the manufacturing process ofthe present invention.

[0065] The nonwoven fabric according to the present invention, even whenthe nonwoven fabric contains the elastic fiber, allows the smooth touchof the nonwoven fabric to the article wearer's skin to be adjusted byplacing in the vicinity of each of the elastic fiber at least oneinelastic fiber which is longer than the elastic fiber. The smooth touchto the article wearer's skin can be effectively adjusted by placing aplurality of the inelastic fibers in the vicinity of the elastic fiberso as to surround this elastic fiber. Since the segment of the inelasticfiber defined between a pair of the neighboring attaching areas in whichthe inelastic fiber is inseparably attached to the elastic fiber islonger than the associated segment of the elastic fiber, the elasticstretchability of the elastic fibers as well as the nonwoven fabric isnot disturbed by the inelastic fiber.

[0066] The process according to the present invention for making thenonwoven fabric is primarily characterized in that the conjugated fibersconsisting of the elastic fibrous component and the inelastic fibrouscomponent separably attached to the surface of the elastic fibrouscomponent are split into the respective fibrous components so that theinelastic fibers having a smaller fineness may surround the elasticfiber having a larger fineness. In this way, the process according tothe present invention can provide thin nonwoven fabric which iselastically stretchable and contractible and allows also at least one ofthe upper and lower surfaces of the nonwoven fabric to present a smoothtouch and high slip properties of the inelastic fiber having a smallerfineness instead of those of the elastic fiber having a larger fineness.

What is claimed is:
 1. An elastically stretchable nonwoven fabriccomprising elastically stretchable first fibers made of a first polymerand inelastically stretchable second fibers made of a second polymer,said nonwoven fabric being characterized by that: said nonwoven fabrichas first and second surfaces as viewed in its thickness direction, saidfirst and second surfaces extending in parallel to each other, saidsecond fiber is bonded to said first fiber at attaching areas formedintermittently along said first fiber and spaced apart from said firstfiber between each pair of said attaching areas neighboring to eachother, each segment of said second fiber spaced apart from said firstfiber between each pair of said attaching areas neighboring to eachother being longer than an associated segment of said first fiber, andthe number of said second fiber is in a range of 1 to 16 per each firstfiber.
 2. The nonwoven fabric according to claim 1, wherein said firstand second fibers intersect with each other in such a manner that saidfirst fiber lies inside and said second fiber lies outside in one ofsaid first and second surfaces.
 3. The nonwoven fabric according toclaim 1, wherein said first fiber has on its circumferential surfacefirst curved surfaces each bulging radially outward from an axis of saidfirst fiber and second curved surfaces each depressed radially towardsaid axis of said first fiber, said first and second curved surfacesalternately appearing in a circumferential direction of said firstfiber, and each pair of said first curved surfaces neighboring to eachother in said circumferential direction cooperate with said secondcurved surface lying between said pair of said first curved surfacesneighboring to each other to form a groove extending in a longitudinaldirection of said first fiber so that said second curved surface definesa bottom of said groove.
 4. The nonwoven fabric according to claim 1,wherein one of said first and second surfaces has a slip angle of 25° to40°.
 5. The nonwoven fabric according to claim 1, wherein said firstpolymer is selected from the group consisting of thermoplasticpolyurethane and thermoplastic polyurethane containing a lubricant andsaid second polymer is selected from the group consisting ofpolyolefin-based polymer and polyamide-based polymer.
 6. A process formaking an elastically stretchable nonwoven fabric formed by elasticallystretchable first fibers made of a first polymer and inelasticallystretchable second fibers made of a second polymer, said processcomprising steps of: feeding, in a machine direction, a plurality ofconjugated fibers each consisting of a first fibrous component made ofsaid first polymer and a second fibrous component extending in parallelto and releasably attached to a surface of said first fibrous componentand thereby forming a web from said conjugated fibers having a basisweight in a range of 10 to 500 g/m²; forming said web with a pluralityof attaching areas intermittently formed in at least one direction ofsaid machine direction and a cross direction intersecting orthogonallysaid machine direction so that said conjugated fibers can not beseparated one from another at said attaching areas; stretching said webat least in said one direction within an elastic range of the firstfibrous component and under a failure point of said second fibrouscomponent and thereby separating said first and second fibrouscomponents one from another between each pair of said attaching areasneighboring to each other and permanently deforming said second fibrouscomponent; and allowing said web to contract under an elastic recoveryforce of said first fibrous component so that said first fiber isobtained from said first fibrous component, said second fiber isobtained from said second fibrous component and said nonwoven fabric isobtained from said web.
 7. The process according to claim 6, whereinsaid first fibrous component of said conjugated fiber has on itscircumferential surface first curved surfaces each bulging radiallyoutward from the axis of said first fibrous component and second curvedsurfaces each depressed radially toward said axis of said first fibrouscomponent, said first and second curved surfaces alternately appearingin a circumferential direction of said first fibrous component, and eachpair of said first curved surfaces neighboring to each other in saidcircumferential direction cooperate with said second curved surfacelying between said pair of said first curved surfaces neighboring toeach other to form a groove extending in a longitudinal direction ofsaid first fibrous component so that said second fibrous componentextends in parallel to said first fibrous component in said groove. 8.The process according to claim 6, wherein the circumferential length ofsaid conjugated fiber occupied by said second fibrous component is in arange of 40 to 90% of the whole circumferential length of saidconjugated fiber.
 9. The process according to claim 6, wherein thenumber of said second fibrous component constituting said conjugatedfiber is in a range of 1 to 16 per one of said first fibrous component.10. The process according to claim 6, wherein said first polymer isselected from the group consisting of thermoplastic polyurethane andthermoplastic polyurethane containing a lubricant and said secondpolymer is selected from the group consisting of polyolefin-basedpolymer and polyamide-based polymer.